JP3400350B2 - Digital signal transmission equipment - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital signal transmission apparatus for connecting two devices with a cable and transmitting a digital signal from one device to another device.

[0002]

2. Description of the Related Art Conventionally, as a device for connecting two devices with a cable and transmitting a high-speed digital signal, such as a camera, a VTR, and a switcher, as seen in Television Society Journal Vol. 48, No. 10. There is a serial transmission device that serializes and transmits digital signals of video and audio between broadcasting equipment. FIG. 9 is a block diagram of a serial transmission device for transmitting a digital signal between a camera capable of outputting the digital signal and a VTR capable of inputting the digital signal. Hereinafter, the conventional transmission of the digital signal will be described with reference to FIG. The device will be described.

In FIG. 9, 1 is a camera, 2 is a terminal for outputting a 10-bit digital video signal output from the camera 1, and 3 is a 1-bit NRZ (Non Return) parallel signal input from a terminal 2. It is a parallel-to-serial conversion circuit that converts to zero signal. 4 is a scramble circuit for converting an NRZ signal into a scrambled NRZI (Non Return to Zero Inverted) signal, 5 is a cable driver capable of driving a 75Ω coaxial cable, 7 is a 5C2V coaxial cable, and 8 is a coaxial cable 7. It is a waveform equalizer that reproduces the transmission signal before transmission by correcting the signal component attenuated in the process of passing through the coaxial cable 7 with respect to the transmission signal transmitted via the same. 9
Is a descramble circuit for converting a scrambled NRZI signal into an NRZ signal, and 10 is a serial NRZ signal.
Silipara conversion circuit for converting to 0-bit parallel signal,
Reference numeral 11 reproduces a clock synchronized with the reproduced digital signal based on the reproduced digital signal, and converts this clock into the serial-parallel conversion circuit 1
A clock recovery circuit for inputting to 0, and 12 for converting the 10-bit digital signal output from the serial-parallel converting circuit 10 to V
This is a terminal input to TR13.

Next, the operation of the conventional digital signal transmission apparatus configured as described above will be described with reference to FIGS. 5, 6, 7, and 9.

Usually, in order to maintain the image quality for broadcasting, the number of quantization bits is 10 bits as a digital video signal, and the signal rate is 36 MHz when the aspect ratio is 16: 9.
(27 MHz at 4: 3 aspect ratio) is required.
Therefore, the camera 1 outputs a 10-bit, 36 MHz digital signal, which is input from the terminal 2 to the parallel-serial conversion circuit 3. 1 by the parallel-serial conversion circuit 3
0 bit, 36MHz digital video signal is 360
It is converted into a high-speed NRZ serial signal of Mbps.

FIG. 5 is a block diagram of the scramble circuit 4. In FIG. 5, 14a to 14j are D flip-flops, and 15a to 15c are exclusive logic circuits. The clocks of the D flip-flops 14a to 14j are equal to the signal rate of the input digital signal. Therefore, N
When the RZ signal inputted to the scramble circuit, and output generator polynomial ^{(X 9 + X 4 +1)} (X + 1) in accordance with successive symbols '1' or '0' of the continuous is converted into small scrambled NRZI signal. In this way, the transmission signal output to the cable is scrambled NRZI having no DC component.
The signal is formed in order for the receiving side to regenerate the clock necessary for the processing after reception based on this transmission signal, as will be described later. In this way, 360 from the cable driver 5
The Mbps scrambled NRZI signal is output as a transmission signal and is transmitted to the VTR 13 side via the coaxial cable 7.

The frequency characteristic of the coaxial cable is generally as shown in FIG. 7, and the signal passing through the coaxial cable is more attenuated as the frequency becomes higher. Therefore, in the waveform equalizer 8 arranged on the VTR 13 side,
By adding the gain of the frequency characteristic opposite to that of the coaxial cable 7 to the transmission signal after transmission, 360
Reproduce the Mbps digital signal. Actually, in the case of a signal having a signal rate of 360 Mbps, the original digital signal is reproduced by performing gain correction on the signal component up to 360 MHz. The reproduced digital signal is input to the descramble circuit 9. FIG. 6 is a configuration diagram of the descramble circuit 9. In FIG. 6, 16a-1
6j is a D flip-flop, and 17a to 17c are exclusive logic circuits. Contrary to the scramble circuit 4, the input scrambled NRZI signal is descrambled and returned to the original NRZ signal. The restored NRZ signal is further processed by the serial-parallel conversion circuit 10 into the original 10 bits, 3
After being converted to a 6 MHz digital signal, VTR13
Entered in.

As described above, according to this conventional digital signal transmission apparatus, a high-speed digital signal of 360 Mbps can be transmitted up to about 200 m using the coaxial cable which has been conventionally used for analog signal transmission. .

Generally, a digital signal contains a lot of high-frequency components above the fundamental wave component, and if the high-frequency components are radiated to the outside of the equipment, they adversely affect other equipment as noise. Particularly in the case of a digital signal transmission device, the influence of this radiation noise extends over a wide range.

On the other hand, not only broadcasting equipment but also equipment around the world such as general household products that outputs digital signals is rapidly increasing. The signal rates of these devices are increasing year by year, and these digital devices tend to be arranged close to each other. Therefore, a problem of so-called EMI, which is an adverse effect of noise generated by these digital devices on each other, has come to be widely cited. As a result, the standards are being reviewed every year in terms of laws and regulations, and it is necessary to meet even more stringent conditions.

[0011]

However, since the shield effect of the coaxial cable is not perfect, in the above-mentioned conventional digital signal transmission device, the high frequency component of the signal is radiated to the outside of the coaxial cable and the other components near the cable are radiated. There is a problem that the device may be adversely affected such as S / N deterioration and malfunction. In particular, for an analog tuner or the like having a minute signal level as an input level, high-frequency radiation noise output from a transmission device for these digital signals is a great obstacle. Generally, in order to reduce the radiation noise, it is necessary to reduce the amplitude of the transmission signal. In that case, the S / N of the transmission signal itself is deteriorated, which causes a problem such as a transmission error.

The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide a digital signal transmission apparatus capable of significantly reducing radiation noise.

[0013]

[0014]

[0015]

[0016]

According to the present invention of claim 1 , a scramble circuit for converting a digital signal of a signal rate D [bps] output from a first device into a scrambled NRZ serial signal, and N. Is a predetermined natural number and has a stop band pole at a frequency f ₀ [Hz] of (N + 0.3) · D <f ₀ <(N + 0.7) · D, and converts the scrambled NRZ serial signal This is a digital signal transmission device including a low-pass filter that passes the signal and a transmission path that transmits the signal that has passed the low-pass filter to a second device.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings showing the embodiments thereof.

FIG. 1 is a diagram showing the configuration of a digital signal transmission apparatus according to an embodiment of the present invention.
The same components as those in the conventional example are given the same reference numerals. As is apparent from FIG. 1, the present embodiment has a configuration in which a low-pass filter 6 is added to the final stage on the transmission side as compared with the conventional example. The configurations of the scramble circuit 4 and the descramble circuit 9 are the same as the configurations of FIGS. 5 and 6 described in the conventional example, respectively.

FIG. 2 shows the frequency characteristic of the low-pass filter 6. As shown in FIG. 2, the low-pass filter 6 has 5
It has a pole in the stop band at 40 MHz, and the frequency of this pole is set to a value corresponding to 1.5D with respect to the signal rate D = 360 Mbps of the input signal. Further, FIG. 3 shows the configuration of the low-pass filter 6.
In FIG. 3, 19a, 19b and 19c are capacitors,
Each having a capacitance _{C 2/2, C 2/} 2, C 1. Also, 2
0 is a coil having an inductance L ₁ , and 18a,
18b is an input terminal for inputting a digital signal, 21
Reference numerals a and 21b are output terminals. As described above, the low-pass filter 6 is a four-element inductive m-type low-pass filter including a capacitor and a coil. When it is desired to set the pole of the stop band to f ₀ in this induction m type low-pass filter, the values of L ₁ , C ₁ and C ₂ may be calculated according to the following equations.

[0020]

[Formula 1] L ₁ = m / √ (1-m ² ) · R / (πf ₀ )

[0021]

## EQU2 ## C ₁ = √ (1-m ² ) / (4 m) ・ 1 / (πf ₀ R)

[0022]

## EQU3 ## C ₂ = m / √ (1-m ² ) 1 / (πf ₀ R) However, in the above equation, R is the input / output impedance of this low-pass filter, and here R = 75Ω. m =
0.6 and f ₀ = 540 MHz, L ₁ = 33.2n
H, C ₁ = 2.6 pF, C ₂ = 5.9 pF.

Next, the operation of the digital signal transmission apparatus of this embodiment having the above configuration will be described with reference to the drawings.

The process until the digital signal output from the camera 1 is converted into the scrambled NRZI signal is exactly the same as the above-mentioned conventional example. Signal rate is D =
In the case of a 360 Mbps digital signal, the spectrum of the scrambled NRZI signal obtained by scrambling this is 1.5D (= 54) as shown in FIG.
0MHz), 2.5D (= 900MHz), ...
(N + 0.5) · D [Hz] (N: natural number) has a spectrum maximum point.

In FIG. 4, the vertical axis represents the level of each frequency component in decibels with reference to the level of the signal component of 1 MHz. As described above, the required signal band for transmitting this scrambled NRZI signal through the coaxial cable is 36.
Since it is 0 MHz, frequency components higher than 360 MHz can be considered as a source of radiation noise. The peak level of this high-frequency component is about -13 dB at the maximum point of 540 MHz, and has almost the same magnitude as the signal level at 300 MHz.

On the other hand, the spectrum of the transmission signal obtained by passing this scrambled NRZI signal through the low-pass filter 6 is as shown in FIG. From FIG. 8, 540
The high frequency component near MHz is significantly reduced, and as a result, the peak level of the high frequency component is about -27 dB at about 420 MHz, which is about 14 dB lower than that before the input to the low pass filter. The transmission signal with the reduced high-frequency component is input to the waveform equalizer 8 on the receiving side via the coaxial cable 7, and the original digital signal is reproduced. After that, a digital signal can be input to the VTR 13 by the process described in the conventional example.

As described above, the signal rate D = 360 [M
bps] digital video signal is scrambled, so its spectrum has a certain distribution that does not depend on the picture, and this is transmitted through a low-pass filter with the frequency of 1.5D = 540 [MHz] as the stop band pole. Since the signal is generated, the radiation noise emitted from the cable can be significantly reduced by a low-pass filter with a small circuit scale, and the adverse effects such as interference and malfunction on other equipment near the transmission cable can be eliminated. You can

In the above embodiment, the induction m-type low-pass filter is used as the low-pass filter, but the present invention is not limited to this, and any type may be used as long as it has a stop band pole at 540 MHz. It may be.

Further, in the above-mentioned embodiment, the low-pass filter having the characteristic of having a stop band pole at 540 MHz is used, but the pole frequency is set to N as a predetermined natural number.
A frequency f ₀ [Hz] of (N + 0.3) · D <f ₀ <(N + 0.7) · D, for example, when N = 1, 468 <f ₀ <
A similar EM if frequency f ₀ [MHz] between 612
The I effect can be obtained.

In the above embodiment, the low-pass filter having the characteristic of having a pole in the stop band is used.
Frequency f [H where D <f <(M + 1) · D (M is a natural number)
z], for example, 360 <f <720, 720 <f <10
If a low-pass filter having an attenuation amount at any frequency f [MHz] of 80, ...
The I effect can be obtained.

Further, although the coaxial cable is used as the transmission line in the above-mentioned embodiment, the same effect can be obtained when another cable such as a triax cable or a twisted pair wire is used or a plurality of cables are used. It goes without saying that you can do it.

Further, in the above embodiment, the example of the device provided with the scramble circuit was described, but even in the case of transmitting a digital signal between the devices not provided with the scramble circuit, the scramble is performed on the transmission side similarly to the present embodiment. By adding a circuit and a low-pass filter and adding a descramble circuit on the receiving side, the radiation noise emitted from the cable can be significantly reduced.

In the above embodiment, the first device is the camera and the second device is the VTR. However, if the device outputs or inputs digital data,
It is not limited to these.

[0034]

As is apparent from the above description, the present invention has an attenuation amount at a frequency f [Hz] of M · D <f <(M + 1) · D (M is a natural number), and the scrambled NRZ Signal rate D [b converted to serial signal
Since a low-pass filter that passes a digital signal of [ps] is provided, the low-pass filter can be configured with a small circuit scale, and the S / N ratio to other nearby devices can be increased.
It has the advantage that it does not have any adverse effects such as deterioration or malfunction.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a digital signal transmission apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing frequency characteristics of a low-pass filter according to the same embodiment.

FIG. 3 is a configuration diagram of a low-pass filter according to the same embodiment.

FIG. 4 is a scrambled NRZI according to the same embodiment.
It is a figure which shows the spectrum of a signal.

FIG. 5 is a configuration diagram of a scramble circuit according to the same embodiment.

FIG. 6 is a configuration diagram of a descramble circuit in the same embodiment.

FIG. 7 is a diagram showing frequency characteristics of a coaxial cable in a conventional example.

FIG. 8 is a diagram showing a spectrum of a transmission signal in the same embodiment.

FIG. 9 is a configuration diagram of a conventional digital signal transmission device.

[Explanation of symbols]

1 camera 3 Parasitic conversion circuit 4 scramble circuit 5 cable driver 6 low pass filter 7 coaxial cable 8 Waveform equalizer 9 descramble circuit 10 Silipara conversion circuit 11 Clock recovery circuit 13 VTR 14a-14j D flip-flop 15a to 15c Exclusive logic circuit 16a-16j D flip-flop 17a to 17c exclusive logic circuit 19a to 19c capacitors 20 coils

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H04L 25/03 H04B 3/50 H04L 25/49

Claims (3)

(57) [Claims] 1. A signal rate D output from the first device.
The digital signal of [bps] is scrambled NRZ
Scramble circuit for converting to a serial signal of (N + 0.3) D <f ₀ <(N +
0.7) · D, which has a pole in the stop band at a frequency f ₀ [Hz] and passes the converted scrambled NRZ serial signal, and a signal which has passed through the low pass filter as a second device. A transmission device for transmitting a digital signal, comprising: 2. The digital signal transmission apparatus according to claim 1, wherein the natural number N is 1. Wherein said transmission path, according to claim 1, characterized in that a coaxial cable or triax cable
Alternatively, the digital signal transmission device according to item 2 .